Audio relay system



Oct. 5, 1965 J. F. LAWRENCE, JR 3,210,612

AUDIO RELAY SYSTEM Filed July 15, 1962 Annu I .l u

United States Patent O I 3,210,612 AUDIO RELAY SYSTEM James F. Lawrence, Jr., 465 Sequoia Drive, Pasadena, Calif. Filed July 13, 1962, Ser. No. 209,673 11 Claims. (Cl. 317-142) My invention relates generally to relay systems and, more particularly, to an audio relay system having a delayed relay release following removal of an audio input signal to the system.

In an audio relay system, a relay is normally energized and actuated when an audio input signal is applied to the system. The relay is provided to control external circuits tor devices according to the actuation of the relay. The relay, for example, can be used to cause an alarm to operate in the event of failure of a monitored program. In this instance, it is desirable that the relay be immediately actuated when an audio signal is applied to the input of the audio relay system to prevent operation of the alarm and that the relay remain actuated so long as the audi-o input signal is applied to the system. The relay, however, should not be responsively actuated by false input signals which are not true audio signals of the program. Since there will also exist various gaps in which there is a total absence of an audio input signal due to silent program intervals, the relay should release only after a suitable predetermined time interval which is greater than any of the silent intervals of the program.

For different types of programs, the maximum time interval required before release of the relay will, of course, be different. The release time of the relay should, therefore, be adjustable over a relatively wide range. In certain applications, a consistent release time of the relay following removal of the audio input signal to the audio relay system is also required for precise control of external circuits or devices.

Bearing in mind the foregoing, it is a major object of my invention to provide an audio relay system in which the controlled relay is immediately actuated when an audio input signal is applied to the system, and release time of the relay following removal `of the audio input signal is easily adjustable over a wide time range.

Another object of the invention is t-o provide an audio relay system having a consistently accurate release time of the controlled relay following periodically recurrent removal of the audio input signal to the system, for any particular release time adjustment setting of the system.

A further object of the invention is to provide an audio relay system which is responsively actuated at a very low input signal level but not by false input signals which are not true radio signals of a monitored program, for example.

A still further obect of this invention is to provide a relay system which is adjustable to produce a very long delayed relay release following removal of an input signal to the system.

Briefly, and in general terms, the foregoing `and other objects are preferably accomplished by providing an audio relay system comprising a combination of an amplifier, a thyratron circuit, a photoconductive time delay control circuit, and a controlled relay. An audio input signal is applied to the amplifier and the amplified signal is used to activate the thyratron circuit. When the thyratron circuit is activated, the controlled relay is immediately ac- .tuated and the photoconductive time delay control circuit is energized. The relay remains actuated and relay release is delayed a predetermined length of time following removal of the audio input signal to the system according to the adjustment of the photoconductive time delay control circuit.

3,210,612 Patented Oct. 5, 1965 My invention will be more fully understood, and other objects and advantages of the invention will become apparent, from the following description of an illustrative example of the invention, to be taken in conjunction with the attached drawing, in which:

FIG. 1 is a circuit diagram of a preferred embodiment of an audio relay system;

FIG. 2 is a graph showing curves for relay release time following removal of the audio input signal to the system, as a function of capacitance connection in the photoconductive time delay control circuit of the system; and

FIG. 3 is another graph illustrating a plot of input sensitivity of the system of FIG. 1 as a function of the input signal frequency.

The audio relay system shown in FIG. 1 has an isolated input provided by transformer T1 having a primary winding Tla and a secondary winding Tlb. Input terminal L1 is connected to one end of the primary winding Tla, input terminal L2 is connected to the other end through a resistor R1, and input terminal L3 is connected directly to the other end of the primary Winding Tla. The resistances of the primary winding Tla and the resistor R1 are each 10K ohms, for example. An audio input signal applied to terminals L1 and L2 will thus see a 20K ohms input which is isolated from ground.

A potentiometer R2 is connected to the secondary winding Tlb and the adjustable tap of the potentiometer R2 is connected to the control grid of a triode section Vla of a dual triode V1, as shown in FIG. 1. The cathode of the triode section Vla is connected to ground through a resistor R3, and the anode is connected to a positive supply voltage B-lthrough resistor R4. The anode Iof the triode section Vla is connected to the control grid of the other triode section Vlb through a coupling capacitor C1. The control grid of the triode section Vlb is connected to ground through grid resistor R5 and a capacitor C2 connected in parallel with the resistor R5.

The cathode of the triode section Vlb is connected directly to ground, and the anode is connected to a positive supply voltage B-lthrough load resistor R6. The anode of the triode section V1b is also connected to the control grid of a thyratron V2 through a series combination of coupling capacitor C3 and limiting resistor R7. A resistor R8 connects the common junction of capacitor C3 and resistor R7 to ground.

The cathode of the thyratron V2 is connected to ground through a resistor R9 and also through a series combination including resistor R10 and neon lamp N1. The anode of the thyratron V2 is connected to an A C. source, and the screen grid is connected to a positive voltage source B-jthrough a resistor R11. The screen or shield grid of the thyratron V2 is also connected directly to the cathode of the thyratron, as shown in FIG. 1.

The cathode of the thyratron V2 is connected by diode D1 to a common terminal L4, of a series including the terminals L5, L6, L7 and L8, through a small resistor R12 which limits the diode surge current. The cathode of the thyratron V2 is also connected by another diode D2 to the control coil Kla of relay K1 through a filter resistor R13. Filter capacitor C4 connects the diode D2 to ground, as shown. The relay K1 is illustrated as having its pole Klb connected to terminal L9, normally closed contact Klc connected to terminal L10, and normally open contact Kld connected to terminal L11.

Capacitors C5, C6, C7 and C8 are respectively connected to the terminals L5, L6, L7 and L8. The capacitors C5 through C8 are all connected to ground, as shown in FIG. 1. These capacitors each have a different value. For example, the values of capacitors C5, C6, C7 and C8 are respectively 20, 40, 60 and 80 mfds. One or more of the capacitors can be connected in parallel to the terminal L8 by suitable jumpers, such as the jumper J connecting the common terminal L4 to terminal L7. A selectively variable capacitance is thus connected to the common terminal L4.

A resistor R14 is also connected to common terminal L4 to be in parallel with the capacitance selectively connected thereto. The resistor R14 has an adjustable tap to which is connected resistor R15 so that the latter resistor is in parallel with a portion of the resistor R14. A variable resistance is thus provided in parallel with the capacitance selectively connected to the common terminal L4. This variable resistance is adjusted to vary the discharge time of the capacitance selectively connected to the common terminal L4.

A series combination of a xed resistor R16 and neon lamp N2 is connected in parallel with the adjustable resistor R14. The lamp N2 will be energized according to the voltage of the capacitance connected to common terminal L4. For the connection indicated in FIG. l, the voltage existing across the capacitor C7 must be suciently high in order that the lamp N2 will be energized and then be at least sufficiently high to maintain energization of the lamp N2.

The lamp N2 is located in proximity to a photoconductive cell R17. The cell R17 connects the common junction of two series resistors R18 and R19 with the common junction of resistor R13 and relay coil Kla. The upper end of resistor R18 is connected to a positive voltage supply B+ and the lower end of resistor R19 is connected to ground. The voltage across the resistor R18 is thus supplied to the control coil Kla of the relay K1 through the photoconductive cell R17.

The resistance of the photoconductive cell R17 is varied from a very high value to a relatively low value when the cell R17 is illuminated by the light output of the energized lamp N2. The negligible current which flows in the control coil Kla is increased to actuate the relay K1 so that the pole Klb engages the contact Kld. The circuit connected to terminals L9 and L10 is opened so that an alarm device (not shown) connected in the circuit remains deenergized so long as the relay Klis actuated..

A tabulation of component types and values for the preferred audio relay system shown in FIG. 1 is given below. The component types and values in this listing are, of course, illustrative and not to be considered as limiting the invention in any manner.

A.C 120 volts, 60 c.p.s. B+ 240 volts. D1, Dz 1N1095. N1, N2 NESl.

R17 Clairex 505L. V1 12AX7.

C1 .0015 mid. C2 .0005 mfd. C3 .01mfd. C4 1 mid.

C5 20 mfd. C6 40 mfd. C7 60 mfd. ,C8 8-0 mfd. R1 10K ohms. R2, R19 100K ohms. R3 1K ohm. R4, R6, R11, R16 220K ohms. R5 2.2M ohms. R7, R10 70K ohms. VR8 47K ohms. R9 12K ohms. R12 10 ohms. R13 4.7K ohms. R14 1M ohm. R15 22K ohms. R18 8.2K ohms.

During normal operation, an audio input signal is applied to terminals L1 and L2. This signal is transformed by transformer T1 and amplified by tube V1 to provide an output signal to the control grid of the thyratron V2. The potentiometer R2 provides gain control for the system and the setting of the adjustable tap should be advanced as far as possible Without causing relay actuation from background noise. A minimum input signal voltage of .005 volt, for example, is required by the system to fire the thyratron V2 and cause relay actuation. The system is not overloaded from an excessive input signal voltage.

The thyratron V2 is fired for an input signal voltage of at least the minimum input signal voltage, and the thyratron V2 conducts during alternate half cycles of the A.C. supply to the thyratron. The lamp N1 is energized when the thyratron V2 conducts and ashes when a normal audio input signal is present. The flashing rate is determined by the presence and absence rate of the audio input signal, or the variation of the audio input signal above and below the minimum input signal voltage needed to re the thyratron V2. When the audio input signal is present continuously above the minimum input signal voltage for tiring the thyratron, the lamp N1 flashes at the frequency of the A.C. supply c.p.s.) which is not very discernible by the eye because of the persistence of vision.

If the lamp N1 flashes only occasionally on fairly constant program material which produces an audio signal that is present and absent or varying at an ordinary rate, the gain control adjustment of potentiometer R2 may be set too loW. Flashing of lamp N1 during program periods of no audio input signal indicates that the gain setting of the potentiometer R2 is too high and that the thyratron V2 is being operated by background noise.

The output of the thyratron is rectified by diodes D1 and D2. The output of the diode D1 is used to charge the capacitor C7, for the capacitance connection indicated in FIG. l. At the same time, the output of diode D2 immediately energizes the control coil Kla and causes actuation of the relay K1. After the capacitor C7 is charged sufficiently to the ionization voltage of the neon lamp N2, the lamp N2 conducts and produces a light output which reduces the very high resistance of the photoconductive cell R17 to a relatively low value. The voltage across resistor R19 is thus also supplied to energize the control coil Kla of the relay K1. This voltage maintains the relay K1 actuated after removal or absence of the audio input signal for a predetermined release time according to the selection and connection of capacitors C5 through C8 to the common terminal L4, and the adjustment of potentiometer R14.

Selection of a range of release time is initially made and accomplished by the connection of various combinations of the capacitors C5 through C8 to the common terminal L4. The graph of FIG. 2 illustrates the ranges of release time which are obtained as a function of capacitance connection to the common terminal L4. The curve MA is a plot of relay release time as a function of capacitance connection at the maximum setting of potentiometer R14, and curve MI is a plot of relay release time as a function of capacitance connection at the minimum setting of po.- tentiometer R14. It can be seen from FIG. 2 that a range from 2.5 to 26 seconds, approximately, is available With a capacitance of 60 mfd. connected to the common terminal L4 of FIG. 1.

The connection of the selected capacitance from capacitors C5 through C8 is made initially, and adjustment of potentiometer R14 to obtain a desired relay release time can be made any time after the audio input signal is applied to the input terminals L1 and L2. A relatively low direct voltage is provided at common terminal L4 when the thyratron V2 is oit; however, this voltage is increased towards the peak voltage of the A.C. supply when the thyratron V2 is conducting. After the charging of the capacitor C7, when the thyratron V2 is cut off` as by removal or absence of the audio input signal to the system, the charged voltage on capacitor C7 discharges through the resistors R14 and R15, and the lamp N2 will be extinguished when the capacitor voltage drops below the maintaining voltage for the lamp. The time constant of the discharge circuit is determined by the setting of potentiometer R14 and the capacitance connected at the common terminal L4 so that relay release time is precisely set by the adjustment of potentiometer R14 with the value of the fixed capacitor C7. lf it is desired to cause the relay K1 to remain released after drop out has occurred, the audio input signal can be locked out by connecting terminal L3 to L1.

The minimum audio input signal voltage which would fire the thyratron V2 and cause actuation of relay K1 was, for example, .005 volt. The graph of FIG. 3 shows a plot of the minimum input voltage to the preferred system required for relay actuation as a function of the frequency of the input signal or voltage. This minimum input voltage of .O05 volt is seen from FIG. 3 to be effective from 700 to 2500 c.p.s., approximately. A decrease in sensitivity below 1000 c.p.s. and above 7000 c.p.s. is provided to reduce false triggering from turntable rumble and hum on the low end, and tape and thermal noise on the high end, for example.

If a wider response band is desired, the values of the coupling capacitors C1 and C3 can be increased to lower the low frequency response. High frequency response can be increased by removing the capacitor C2 from the input circuit of the triode section Vlb.

It is to be understood that the particular embodiment of my invention described above and shown in the drawing is merely illustrative of and not restrictive on the broad invention and that various changes in design, structure and arrangement may be made without departing from the spirit and scope of the broader of the appended claims.

I claim:

1. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a source of power for energizing said coil;

a photosensitive cell for controlling power from said source to said coil, said cell permitting power from said source to energize said coil when said cell is illuminated;

a light-producing device for illuminating said cell, said light-producing device producing a light output and illuminating said cell when said light-producing device is energized;

a capacitor of variable capacitance;

means for connecting said light-producing device to said capacitor;

means for providing a voltage to lsaid capacitor and said light-producing means, said voltage charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell and energize said coil; and

a resistor of Variable resistance connected to said capacitor for controlling discharge rate of said capacitor, l

whereby said light-producing device is maintained energized by said charged capacitor after removal of said voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

2. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a first source of power for energizing said coil;

a photoconductive cell for controlling power from said first source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a gaseous discharge lamp for illuminating said cell, said lamp producing a light output and illuminating said cell when said lamp is energized;

a capacitor of variable capacitance;

means connecting said lamp to said capacitor;

a second source of power for charging said capacitor to an ionizing voltage which energizes said lamp; switching means operable to connect said second source to said capacitor, to charge said capacitor to said ionizing voltage which energizes said lamp; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after disconnection of said second source from said capacitor at the end of an operation of said switching means,

whereby said lamp is maintained energized by said charged capacitor afted disconnection of said second source for a predeterminted length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

3. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a first source of power for energizing said coil;

a photosensitive cell for controlling power from said source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a light-producing device for illuminating said cell, said light-producing device producing a light output and illuminating said cell when said light-producing device is energized;

a capacitor of variable capacitance;

means for connecting said light-producing device to said capacitor;

a second source of power;

means operable to connect said second source to said coil of said relay and to said capacitor, for directly energizing said coil which actuates said relay and charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after disconnection of said second source from said capacitor at the end of an operation of said operable means,

whereby said light-producing device is maintained energized by said charged capacitor after disconnection of said second source for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

4. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a first source of power for energizing said coil;

a photosensitive cell for controlling power from said source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a light-producing device for illuminating said cell, said light-producing device producing a light output and illuminating said cell when said light-producing device is energized;

a capacitor of variable capacitance;

means for connecting said light-producing device to said capacitor;

a second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage;

means for applying said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

means for applying said thyratron output voltage to said capacitor, for charging said capacitor to an exciting Voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said light-producing device is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

5. A relay system having a delayed relay release,

comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a r'st source of power for energizing said coil;

a photoconductive cell for controlling power from said iirst source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a gaseous discharge lamp for illuminating said cell, said lamp producing a light output and illuminating said cell when said lamp is energized;

a capacitor of variable capacitance;

a second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage; means for applying said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

means for applying said thyratron output voltage to said capacitor, for charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor 'for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said lamp is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

6. A relay system having a delayed relay release,

comprising:

a relay including a control for actuating said relay when said coil is energized;

a irst source of power for energizing said coil;

a photosensitive cell for controlling power from said source to said coil, said cell permitting power from said rst source to energize said coil when said cell is illuminated;

a light-producing device for illuminating said cell, said light-producing device producing a light output and illuminating said cell when said light-producing device is energized;

a capacitor of variable capacitance;

means for connecting said light-producing device to said capacitor;

a second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage;

a first diode connected to apply said thyratron output voltage to said coil of said relay, for directly energizing said coil to ,actuate said relay;

a second diode connected to apply -said thyratron output voltage to said capacitor, for charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of Isaid thyratron output voltage at the end of an operation of said thyratron,

whereby said light-producing device is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

7. A relay system having a delayed relay release,

comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a first source of power for energizing said coil;

a photoconductive cell for controlling power from said rst source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a gaseous discharge lamp for illuminating said cell,

said lamp producing a light output and illuminating said cell When said lamp is energized;

capacitor oi variable capacitance;

second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage;

a iirst diode connected to apply said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

a second diode connected to apply said thyratron output voltage to said capacitor, for charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said lamp is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

8. A relay system having a delayed relay release,

comprising:

a relay including a control coil for actuating said relay when -said coil is energized;

a first source of power for energizing said coil;

a photosensitive cell for controlling power from said source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a light-producing device for illuminating said cell,

said light-producing device producing a light output and illuminating said cell when said light-producing device is energized;

a capacitor of variable capacitance;

means for connecting said light-producing device to said capacitor;

a second source of power;

a thyratron connected to said second source and loperably energizable to provide an output voltage; means for applying an input signal to said thyratron, said thyratron being operably energized by at least a predetermined magnitude of said input signal;

means for applying said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

means for applying said thyratron output voltage to said capacitor, for charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said light-producing device is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

9. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a first source of power for energizing said coil;

a photoconductive cell for controlling power from said first source to said coil, said cell permitting power from said lirst source vto energize said coil when said cell is illuminated;

a gaseous discharge lamp for illuminating said cell, said lamp producing a light output and illuminating said cell when said lamp is energized;

a capacitor of variable capacitance;

a second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage; means for applying an input signal to said thyratron, said thyratron being operably energized by at least a predetermined magnitude of said input signal;

means for applying said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

means for applying said thyratron output voltage to said capacitor, for charging said capacitor to an eX- citing voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said lamp is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

10. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a first source of power for energizing said coil;

a photosensitive cell for controlling power from said source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a light-producing device for illuminating said cell, said light-producing device producing a light output and illuminating said cell when said light-producing device is energized;

a capacitor of variable capacitance;

means for connecting said light-producing device to said capacitor;

a second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage;

means for amplifying an input signal and applying the amplified signal to said thyratron, said thyratron be ing operably energized by at least a predetermined magnitude of said input signal;

a first diode connected to apply said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

a second diode connected to apply said thyratron output voltage to said capacitor, for charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said light-producing device is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time according to selected values of said capacitor and resistor, to illuminate said cell and energize said coil to actuate said relay.

11. A relay system having a delayed relay release, comprising:

a relay including a control coil for actuating said relay when said coil is energized;

a lirst source of power for energizing said coil;

a photoconductive cell for controlling power from said first source to said coil, said cell permitting power from said first source to energize said coil when said cell is illuminated;

a gaseous discharge lamp for illuminating said cell, said lamp producing a light output and illuminating said cell when said lamp is energized;

a capacitor of variable capacitance;

a second source of power;

a thyratron connected to said second source and operably energizable to provide an output voltage;

means for amplifying an input signal and applying the amplified signal to said thyratron, said thyratron being operably energized by at least a predetermined magnitude of said input signal;

a first diode connected to apply said thyratron output voltage to said coil of said relay, for directly energizing said coil to actuate said relay;

a second diode connected to apply said thyratron output voltage to said capacitor, for charging said capacitor to an exciting voltage which energizes said light-producing means to illuminate said cell; and

a resistor of variable resistance connected to said capacitor for controlling discharge rate of said capacitor after removal of said thyratron output voltage at the end of an operation of said thyratron,

whereby said lamp is maintained energized by said charged capacitor after removal of said thyratron output voltage for a predetermined length of time aC- cording to selected values of said capacitor and resistor, illuminate said cell and energize said coil to actuate said relays.

References Cited by the Examiner UNITED STATES PATENTS tronic Dryers, copyright 1960, Maytag Co. Service Dept.

SAMUEL BERNSTEIN, Primary Examiner. 

1. A RELAY SYSTEM HAVING A DELAYED RELAY RELEASE, COMPRISING: A RELAY INCLUDING A CONTROL COIL FOR ACTUATING SAID RELAY WHEN SAID COIL IS ENERGIZED; A SOURCE OF POWER FOR ENERGIZING SAID COIL; A PHOTOSENSITIVE CELL FOR CONTROLLING POWER FROM SAID SOURCE TO SAID COIL,S AID CELL ERMITTING POWER FROM SAID SOURCE TO ENERGIZE SAID COIL WHEN SAID CELL IS ILLUMINATED; A LIGHT-PRODUCING DEVICE FOR ILLUMINATING SAID CELL, SAID LIGHT-PRODUCING DEVICE PRODUCING A LIGHT OUTPUT AND ILLUMINATING SAID CELL WHEN SAID LIGHT-PRODUCING DEVICE IS ENERGIZED; A CAPACITOR OF VARIABLE CAPACITANCE; MEANS FOR CONNECTING SAID LIGHT-PRODUCING DEVICE TO SAID CAPACITOR; MEANS FOR PROVIDING A VOLTAGE TO SAID CAPACITOR AND SAID LIGHT-PRODUCING MEANS, SAID VOLTAGE CHARGING SAID CAPACITOR TO AN EXCITING VOLTAGE WHICH ENERGIZES SAID LIGHT-PRODUCING MEANS TO ILLUMINATE SAID CELL AND ENERGIZE SAID COIL; AND A RESISTOR OF VARIABLE RESISTANCE CONNECTED TO SAID CAPACITOR FOR CONTROLLING DISCHARGE RATE OF SAID CAPACTOR, WHEREBY SAID LIGHT-PRODUCING DEVICE MAINTAINED ENERGIZED BY SAID CHARGED CAPACITOR AFTER REMOVAL OF SAID VOLTAGE FOR A PREDETERMINED LENGTH OF TIME ACCORDING TO SELECTED VALUES OF SAID CAPACITOR AND RESISTOR, TO ILLUNINATE SAID CELL AND ENERGIZE SAID COIL TO ACTUATE SAID RELAY. 